socketpair

SYNOPSIS
#include <sys/types.h> /* See NOTES */
#include <sys/socket.h>
int socketpair(int domain, int type, int protocol, int sv[2]);
DESCRIPTION
The socketpair() call creates an unnamed pair of connected sockets in
the specified domain, of the specified type, and using the optionally
specified protocol. For further details of these arguments, see
socket(2).
The descriptors used in referencing the new sockets are returned in
sv[0] and sv[1]. The two sockets are indistinguishable.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
ERRORS
EAFNOSUPPORT
The specified address family is not supported on this machine.
EFAULT The address sv does not specify a valid part of the process
address space.
EMFILE Too many descriptors are in use by this process.
ENFILE The system limit on the total number of open files has been
reached.
EOPNOTSUPP
The specified protocol does not support creation of socket
pairs.
EPROTONOSUPPORT
The specified protocol is not supported on this machine.
CONFORMING TO
4.4BSD, POSIX.1-2001. The socketpair() function call appeared in
4.2BSD. It is generally portable to/from non-BSD systems supporting
clones of the BSD socket layer (including System V variants).
NOTES
On Linux, the only supported domain for this call is AF_UNIX (or syn-
onymously, AF_LOCAL). (Most implementations have the same restric-
tion.)
Since Linux 2.6.27, socketpair() supports the SOCK_NONBLOCK and
SOCK_CLOEXEC flags described in socket(2).
POSIX.1-2001 does not require the inclusion of <sys/types.h>, and this
header file is not required on Linux. However, some historical (BSD)
Linux 2008-10-11 SOCKETPAIR(2)